Electronic tube



April 1, 1941. o. T. MCILVAINE 2,236,647

ELECTRONIC TUBE Original Fild Jan. 6, 1932 INVENTOR ATTORNEY PatentedApr. 1,1941

ELECTRONIC TUBE Oran T. Mcllvalne, Geneva, 11].

' Application January 6, 1932, Serial No. 584,967

' Renewed December 15, 1937 8 Claims. (01. 250-165) This inventionrelates to electronic tubes and has among its objects the provision or adevice of this character wherein an increased vigor of electronicemission is secured per unit of energizing intensity, either heat orlight as the case.

metric in its action; the provision of an improvedmethod of sensitizingor energizing such a tube; the provision of a new and improvedcomposition of matter for effecting sensitization of such a tube; whilefurther objects and advantages o; the invention will become apparent asthe description proceeds.

In thedrawing accompanying and forming a part of this application Fig. 1is a perspective view partly in section of an unfinished tube ofpreferred form containing my improvements although it will be understoodthat the tube in question is capable of very great modifications in theshape, size, arrangement, number, position, and relation of its activeelements; Fig. 2 is a side elevation of a modified type of tubecontain-r.

ing my improvements; and Fig. 3 is a section through a capsule ofconvenient shape together with its mounting.

In the particular embodiment here shown a.

cathode .l and anode 2 are carried by a press 3,;

sealed in the stem 6 of a glass-globe 5 and pro vided with leading-inwires 6. Any suitable or desirable kind of base can be employed.

In the embodiment shown in Fig. 1 the photoelectrode or cathode lconsists of a metal plate of substantially semi-cylindrical shape havingthe slties tend to produce smoothly plated surfaces while high currentdensities tend to produce rough or mat surfaces, as is well understoodby those skilled in the art. The anode can be of the same substance orany other conductive material, copper or nickel being especiallydesirable.

The energizing substance consists of a caesium compound mixed with oneor more elemental substances of a type which react therewith at a red orwhite heat, but not at a lower temperature, to reduce the caesiumcompound to metallic caesium with the generation of reaction-prodanode 2substantially coinciding with its axis.

This plate is carried by an upright post I. the

two electrodes being connected at their upper ends by a glass bridge 8by which they are steadled, one of the parts also carrying .a tinyhollowmetallic capsule 9 in which the energizing substanc or material isintroduced. The cathode is preferably made, at least superficially, ofsilver and this preferably in a mat form. It may be a plate of puresilver, or it may equally well be a plate of base metal such as copperor nickel (or nickel-plated copper). electro-pla-ted externally withsilver. One well known method of accomplishing the, production of a matsurface r on an electio-plated article is by using a plating I bath ofsilver cyanide. During the plating operation the current density isadjusted to the point where the desired character of surface is obtainedon the plated article." Low current denucts which are wholly solid. Theemployment of caesium as an energizing agent is not uncommon, nor is theemployment of caesium produced by-reaction, but 'a common procedure inthe past has been to employs. reaction between caesium chloride andmetallic calcium, thus producing calcium chloride and metallic caesium.Such mixture and reaction is unsatisfactory for two 'reasons: first,because caesium chloride tends readily to absorb water vapor whichitis'dimcult or impossible to remove completely, and because the reactionbetween the calcium and-the caesium chloride occurs at such lowtemperature as to render it impossible to heat the tube and its elementsto a sufiicient temperature to remove the oocluded water vapor and othergases.

Accordingly an important featureof my invention is the employment ofsuch an elemental substance in combination with such a compound ofcaesium that the reaction shall only occur at a temperature above thatnecessary for the successful outgasslng otthe tubes and the metallicelements and'the energizing substance itself and this with theproduction of reactionproducts which are wholly solid, the ingredientsalso being of a non-hygroscopic nature. These considerations clearlyeliminate all the gaseous, liquid, and easily fusible elements, allalkaliand alkalineearth metals, all carbon, hydrogen, and halogencompounds, and leave in effect only oxygen-caeslum compounds for thesubject, and the highermelting-point, oxygen-avid metals and metaloidsas-the reactive agents. The last-named limitat-lon essentiallyeliminates such metals as copper, gold platinum, silver and theiron-group metals, none of which have a strong affinity for oxygen.Aluminumlles nearly on the border line, being unsatisfactory ln'that itsreaction tends to begin. at too low a temperature and to proceed withundue vigor, although itcan' be employed in some cases if sufllclentlydiluted by restraining agents. Substances like boron, molybdenum,

and titanium are much better, but I prefer silicon above all; and forthe caesium compound I prefer the chromate, inasmuch as it has asufficiently high melting point, does not decompose or sublime whileheating, is not hygroscopric, and produces, upon reaction with thesubstances mentioned, only solid non-volatile oxides. I donot limitmyself to this one compound of caesium since other oxygen compoundsthereof can be employed, such as the phosphate.

The preferred procedure is as -follows: the caesium compound chosen,together with the reaction agent are mixed intimately together,preferably inthe proper molecular proportions, and introduced into thecapsule I, which is made with a cavity for the purpose, the edges beingclosedby folding or spot-welding so as to hold the un reacted materialswhile allowing escape of volato a yellowish color, often streaked ordiscolored with brown. Carried further than this the next color producedis a brown, alsogiving good tilized caesium. The various elements areintroduced and sealed into the glass globe, the air exhausted by way ofthe pipe ll provided for the purpose, heat is applied in any suitableway to drive off the absorbed gases from the glass and from the tubeelements, and a small amount of dry air (oxygen) is admitted, afterwhich a unidirectional, high-tension current is passed be-- glass as theformer permits the passage of more of the ultra violet rays than doesthe latter, and

I use either a vacuum or a gas-filling. Argon is good when gas is to beused, the pressures employed being up to a few mm. of mercury; 2/10 mm.pressure is very satisfactory, but either more or less canbe used.

As an example of a different arrangement I have shown in Fig. 2 athree-element tube comtween the anode and the cathode, from an inductioncoil or other uni-directional source whereby all combined oxygen isremoved from the anode, and the surface of the cathode is covered withoxidized silver. The gases are then exhausted with the employment ofsufficient heat to outgas the glass and metal and energizing substancewithout however producing the re. action of such substance.

Sufllcient heat is then concentrated, upon the capsule to produce areaction between the substances therein, which in the preferred caseconsist of caesium chromate andsiliwmthe reaction products consisting ofmetallic camium on the one hand and oxides of chromium and silicon onthe other hand. The heating may be effected by a burning glass or by ahigh-frequency inductionf-urnace, and requires a bright red heat. Itoccurs without undue vigor, although a slight intensification of rednessis'visible at the instant of reaction. A distinct advantage of thedescribed composition in the case of a photo electron tube is that theglass walls are left unobscured. The tube and its contents are now al-'.lowed to cool.

The leading-in wires are next connected'to a suitable biasing battery incircuit with a microammeter and heat is applied. to the tube bysurrounding it with an internally heated jacket or other suitable means.As a result 'otthe chemical reaction above described the metalliccaesium will have become-disseminated widely througtn out the tube andupon cooling will have condensed on all parts of the same. The purposeof the heating is two-fold: first, to volatilize the caesium which hasbecome deposited elsewhere than 'upon the cathode, by which alone it isabsorbed and retained, due to the oxidation of the silver which issupposed to react in some way with the caesium; a second object of theheating is to produce the described reaction between the metalliccaesium and the silver oxide. 'Ihis.re-' actionapparently varies withthe temperature and is signalized by a continuous change in color of thecathode, and by a constant vibration of the ammeter needle as thetemperature of the tube is gradually raised. The heating is stopped atthe pointat which the cathode exhibits the prising a photo-electrode ii,an anode It, and a thermionic-electrode II (here consisting of anemissive element), the photo-electrode- II also constituting a grid. Theprocedure hereabove described may be employed for energizing this tube,the grid being first plated with silver before assembling, and oxidisedduring the pumping operation. .Thisoxidation is confined entirely to thephoto-electrode or grid by the electrical protection of the otherelements. The remaining steps are similar. to those hereinbeforedescribed. Such a tube, when subjected to. a

. light-beam, will control passage of electrons from thethermionic-electrode It to the anode II in accordance with the intensityof the light-beam.

A similar mode of operation could of course be obtained by connecting aseparate thermioniceiectrode'plate to this grid either in the same or adifferent tube. I mention these modifications here to show theflexibility of my process, and how any element out of many ina tube canbe exclusively energised. It will, be understood that the energizingsubstance can be diluted with other substances, either active orinactive, beneflcial or the reverse, without departing from myinvention; for example a quantity of metallic chromium can be mixed withthe other ingredients. Also the plating can be applied to the cathodeonly or to both electrodes, since'it is the oxidizingof the cathodesurface and not its metallic nature which determines the selectiveadhesion of the caesium thereto. Other surfaces than silver areoperative for the purpose, though silver due to the ease with which itis electroplated and the weakness of its aifinity for oxygen isparticularly convenient. Accordingly I, do not limit myself to the formsof elements herein shown, nor the mode of connection thereof, nor theparticular steps or materials described, except as the same are recitedin my several claims which I desire may be construed broadly, eachindependent of limitations contained in other claims.

Having thus described my invention what I I maximumphoto-electric'eifect; this corresponds rough surface activatedby'caesium, the surface assess? 3. The art of manufacturing aphoto-electric cathode comprising the steps of depositing a coating ofoxidizable material on .the surface .of a foundation structure and socontrolling the deposit-as to produce a mat surface on the coating,oxidizing said mat surface, depositing on the oxidized surface a layer,of light sensitive material,

heating the cathode, and stopping the heating when the surface shows adesired color effect approximately between yellow and brown.

4. The process of activating an electrode of a photo-electric tubecomprising the steps of electro-plating acoating of oxidizable materialon the surface of a foundation structure and so controlling theelectro-plating as to produce a mat surface on the coating, introducingsaid electrode into an envelope,.oxidizing the mat surface of saidelectrode, depositing on the oxidized surface a layer of light sensitivematerial, producing a chemical reaction between the oxidized su1;- faceand the light sensitive material by heating the electrode, and stoppingthe heating when the surface shows a desired color effect approximatelybetween yellow and brown.

'5. The process of activating a cathode of a photo-electric tubecomprising the steps of electro-plating a coating of oxidizable materialon the surface of a foundation structure and so controlling theelectro-plating as to produce a mat surface on the coating, introducingsaid cathode and caesium reaction mixture into an envelope, exhaustingsaid envelope, oxidizing the surface of said cathode in the presence ofoxygen, liberating the caesium from said caesium-reaction mixture anddepositing the same on the cathode, heating the cathode, and stoppingthe heating when the cathode shows a desired color efiect approximatelybetween yellow and brown.

6. The process of activating a cathode of a photo-electric tubecomprising the steps of coating a foundation member with silver,producing a mat silver surface on said coating by electroplating,introducing said cathode and a caesium reaction mixture into anenvelope, exhausting said envelope, oxidizing the surface of the cathodein the presence of oxygen, liberating the caesium from said caesiumreaction mixture and depositing the same on the cathode, heating thecathode withthe caesium deposit thereon, and stopping the heating whenthe'cathode' shows a color approximately between yellow and brown.

7. The art of manufacturing a photo-electric cathode comprising thesteps of depositing a coating ofoxidizable material on the surface of afoundation structure and so controlling the'deposit as to produce a matsurface on the coating, oxidizing said mat surface, depositing on theoxidized surface a layer of light sensitive material, producing achemical reaction between the oxidized surface and the light sensitivemateria by applying heat to the cathode, and stopping the heating whenthe surface shows a color efiect approximately between yellow and brown,

8. The process of manufacturing a photo-electrio cathode comprising thesteps of depositing a coating of oxidizable material on the surface of afoundation structure and so controlling the deposit as to produce a matsurface on the coatins. oxidizing said mat surface, depositing on theoxidized surface a layer of light sensitive material, heating thecathode, and stopping the heat-. ing when the surface shows a desiredcolor effect.

ORAN "1', McmvAmn.

